1. Field of the Invention
Embodiments of the invention generally relate to a processing chamber, sensors and controls for conducting an electroless plating process.
2. Description of the Related Art
Metallization of sub-quarter micron sized features is a foundational technology for present and future generations of integrated circuit manufacturing processes. More particularly, in devices such as ultra large scale integration-type devices, i.e., devices having integrated circuits with more than a million logic gates, the multilevel interconnects that lie at the heart of these devices are generally formed by filling high aspect ratio, i.e., greater than about 4:1,interconnect features with a conductive material, such as copper. Conventionally, deposition techniques such as chemical vapor deposition and physical vapor deposition have been used to fill these interconnect features. However, as the interconnect sizes decrease and aspect ratios increase, void-free interconnect feature fill via conventional metallization techniques becomes increasingly difficult. As a result, plating techniques, i.e., electrochemical plating and electroless plating, have emerged as promising processes for void free filling of sub-quarter micron sized high aspect ratio interconnect features in integrated circuit manufacturing processes. Further, plating processes, and in particular, electroless plating processes have emerged as promising processes for depositing post deposition layers, such as capping layers, for example.
However, with regard to electroless plating processes, conventional processing apparatuses and methods have faced substantial challenges in accurately controlling the electroless deposition process and the defect ratios in the resulting deposition layers. Since there is generally no way to know when the electroless process has initiated, and the initiation time varies from substrate to substrate or from one area of a substrate to another it is hard to know when the desired thickness of material has been deposited across the surface of the substrate. Further, monitoring and controlling various process steps, such as rinsing the substrate between electroless deposition process steps or after the process has been completed, can prevent the interaction of incompatible chemistries, reduce cross contamination to subsequent processes, and minimize the amount of wasted time necessary to assure the substrate has been sufficiently processed. To compensate for the process variation and unknown processing time, engineers will often use a worst case processing time to assure that a desired amount of material is deposited or the substrate is sufficiently processed. Use of a worst case process time causes the throughput of the processing chamber to suffer and is wasteful of the often expensive electroless deposition solutions, contaminate subsequent process which all lead to substrates variability and possibly scrap. Monitoring and controlling the state of the electroless deposition process is an important part of assuring a uniform layer is deposited with minimal defects.
Therefore, there is a need for an improved apparatus and method for monitoring and controlling various aspects of the electroless deposition process.